let course = document.querySelector('.course');
let ul = document.querySelector('.course ul');
let str = '';
for (let i = 0; i < 6; i++) {
  ul.innerHTML += `
  <li>
     <a>徒手胸肌训练进阶</a>
     <p>男生专属变式俯卧撑训练,在家也能练出钢铁般的胸肌</p>
    </li>
  `;
}
